Field of Endeavor
The present invention relates to a burner of a gas turbine.
Brief Description of the Related Art
In particular the present invention refers to a sequential combustion gas turbine; these gas turbines are known to include a compressor generating a main compressed air flow and feeding it to a first burner.
In the first burner a fuel is injected in the compressed air flow to form a mixture that is combusted and expanded in a high pressure turbine.
The hot gas flow discharged by the high pressure turbine (that still includes a large amount of air) is then fed to a second burner, where further fuel is injected to form a mixture; this mixture is thus combusted and expanded in a low pressure turbine.
A burner embodying principles of the present invention is advantageously the second burner of the sequential combustion gas turbine and is made of a duct (typically with a rectangular, square or trapezoidal shape) housing a conditioning device for guaranteeing a straightened inflow of the hot gas coming from the high pressure turbine.
The duct also has four vortex generators, each extending from one of its walls and arranged to generate vortices within the hot gas flow.
Downstream of the vortex generators, the duct has a lance made of a stem from which a terminal portion extends; the terminal portion is provided with nozzles for injecting the fuel.
The end portion of the duct defines a mixing zone where the fuel injected by the lance mixes with the hot gas flow.
Nevertheless, as the lance is positioned immediately downstream of the vortex generators, its stem at least partially blocks the vortices generated by the upper vortex generator (i.e., the vortex generator projecting from the same wall as the stem of the lance).
This disturbs the structure of the vortices within the burner and, in practice, decreases the total mixing efficiency, causing high NOx emissions.
In addition, the gas flow (which includes a large amount of air), when passing through the duct, is subjected to a large pressure drop, due in particular to the stem of the lance. This worsens the performance of the gas turbine.
Different burners have been developed which face these drawbacks.
U.S. Pat. No. 5,513,982 discloses a burner having vortex generators that have a tetrahedral shape and are provided with holes or nozzles at their side walls. In a different embodiment of the burner of U.S. Pat. No. 5,513,982, the holes or nozzles are placed along all the width of the side walls.
Nevertheless, in both cases, since the fuel is injected from the vortex generators, it enters recirculating regions with very low axial velocity.
Because of the high temperature of the hot gas flow, it auto ignites within the duct (i.e., before entering the combustion chamber located downstream of the duct), damaging the burner.